Visible-Light-Induced Organic-Dye-Catalyzed Bromination of Activated Alkenes with Sodium Bromide

The direct introduction of a bromine atom into organic molecules is valuable because of its versatility in synthetic intermediates and modular building blocks but traditionally suffers from poor selectivity and relatively complicated and/or harsh reaction conditions. We herein present the first visible-light-driven organic-dye-catalyzed bromination protocol under mild conditions with high regioselectivity. This methodology leverages rapid intramolecular radical trapping to achieve regioselective monobromination of alkenes, thus effectively suppressing competing dibromination and electrophilic bromination pathways. By utilizing sodium bromide (NaBr) as a sustainable and cost-effective bromide source, this benign protocol produces diverse bromo-substituted indolo[2,1-a]isoquinolines and γ-carbolinones in good yields. Mechanistic studies provided that the generation of the bromine radical was the pivotal step for this relay reaction.